On December 2, 2014 5:31:13 AM EST, "Carlos E. R." email@example.com wrote:
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On 2014-12-02 07:42, Achim Gratz wrote:
A snapshot is nothing more than telling btrfs "if anything writes to this file, make a copy of it and keep the old data around".
Which is not intuitive: typically a snapshot would be made at the instant of the request, occupying the full needed space. Btrfs snapshots are different, compact and fast. Not a backup snapshot.
I don't find snapshot a well-defined term. There are both COW snapshots and clone snapshots.
I believe most file systems use COW technology to implement snapshots. Linux LVM uses COW.
But there are also lots of systems that implement snapshots as clones. The way I've seen the most is for a mirror to be created, then broken at snapshot time.